As processes for producing carbamates, (1) a process of reacting an isocyanate with an alcohol, (2) a process of reacting a chloroformate ester with an amine in the presence of a base, (3) a process of reacting phosgene with an alcohol and an amine, and (4) a process of reacting urea with an alcohol, are generally known.
However, these conventional processes are disadvantageous in that in the process (1), the isocyanate is stimulative and is difficult to handle; in the process (2), the base must be used in an molar amount equal to or more than that of the reactive compounds; in the process (3), phosgene exhibits a high toxicity and a base must be used for the reaction; and in the process (4), the reaction must be carried out at a high temperature under a high pressure.
On the other hand, as processes for producing aryl carbamates from diaryl carbonates, (5) a process of reacting a diaryl carbonate with an aromatic amine compound in the presence of a heterocyclic monocyclic tertiary amine compound, such as 2-hydroxypyridine, as disclosed in Japanese Unexamined Patent Publication No. 52-136,147, J. Polym. Sci., Polym. Chem. Ed., 17(3), 835 (1979), and Inst. Prog. Urethan, 2, 61 (1980), (6) a process of reacting a diaryl carbonate with an aliphatic amine compound without the presence of a catalyst, as disclosed in U.S. Pat. No. 4,097,676), (7) a process of reacting bis(4-nitrophenyl)carbonate with an aliphatic amine compound and aniline in methylene chloride, as disclosed in Synthesis, 423 (1989), (8) a process of reacting bis(2,4-dinitrophenyl)carbonate with amino acid ester, as disclosed in Chem. Ber., 99, 1576 (1966), (9) a process of reacting an asymmetric bis(nitro-substituted aryl)carbonate with an aliphatic primary amine compound as disclosed in Synth. Commun., 26 (2), 331 (1996), (10) a process of reacting diphenyl carbonate with an aromatic amine compound in the presence of an organic phosphoric acid, trifluoro-methanesulfonic acid, trifluoroacetic acid, propionic acid or an aromatic amine-hydrochloric acid salt, as disclosed in Tetrahedron, 51, 8073 (1995), (11) a process of reacting a diaryl carbonate with a primary or secondary polyamine in the presence of a Lewis acid catalyst, as disclosed in Japanese Unexamined Patent Publication No. 47-11,562, and (12) a process of reacting a diaryl carbonate with an alkylpolyamine, as disclosed in Japanese Unexamined Patent Publication No. 1-230,550, are known.
These processes are, however, disadvantageous in the following problems. In the process (5), the catalyst, which is expensive, must be used in an molar amount equal to or more than the molar amount of the reactive materials, the reaction rate is slow and, when the reaction temperature is raised to increase the reaction rate, urea derivatives are produced, as by-products, in a large amount. In the process (6), when an aromatic amine compound or other amine compound having a high stereostructual volume is used, the reactivity of the amine compound with the diaryl carbonate is very low, and when the reaction temperature is raised to enhance the reactivity of the amine compound, urea derivatives are produced, as by-products, in a large amount. In the process (7), although when the aliphatic primary amine compound is used a relatively good result can be obtained, when the secondary amine compound, which has a high steric hindrance, is used, the reaction rate is slow and, especially, when an aromatic amine (aniline) is used, the reaction rate is very slow and the yield is unsatisfactory. In the process (8), the amino acid ester to be used as a starting material is limited to a primary amino acid ester which can easily react even without the presence of a catalyst. In the process (9), the starting amine compound is limited to an aliphatic primary amine compound. In the process (10), there is a problem in the catalyst usable for the process. Namely, although an organic phosphoric acid is a most effective catalyst, this compound is disadvantageous in that the price is very high. Also, catalysts other than an organic phosphoric acid result in a slow reaction rate. Further, when trifluoroacetic acid or propionic acid is used as a catalyst, these catalyst compounds react with the amine to produce an acid amide, as a by-product, and thus the yield of the target product disadvantageously decreases. Further, in the processes (5), (11) and (12), there are disadvantages in that since a polyamine having two or more amino groups is used, the reaction is carried out in two or more steps, and thus the reaction time is longer than that in the production of the carbamate from the monoamine compound, and by-products (urea derivatives) are easily produced during the reaction steps. Also, in the processes (5), (11) and (12), there are problems that when the reaction temperature is raised to increase the reaction rate, the urea derivatives, and allophanates, biurets and trimers derived from decomposition of the carbamates, are produced and thus the yield of the target compound decreases, and that when the aromatic polyamine compounds or other polyamine compounds having a high stereostructual volume are employed, they exhibit a very low reactivity. Therefore, when the yield of the target compound is low and the by-products are produced, there is an inevitable problem that it is very difficult to isolate the resultant target compound from the reaction product mixture. Further, in the process (11), there is a problem that the reaction vessel is corroded by the Lewis catalyst.
As mentioned above, the conventional carbamate production processes have various problems.
Namely, the processes (1) to (4) have problems derived from the starting materials, namely the starting materials having a high stimulation or toxicity, or the base must be used, or problems derived from reaction conditions, namely the reaction must be carried out at a high temperature or under a high pressure.
The processes (5) and (6) have a problem in that the reactivity is variable in response to the type of the amine compound applied to the reaction, especially when an aromatic amine compounds or other amine compounds having a high stereostructual volume are used, the reactivity decreases and urea derivatives are produced as by-products. Therefore, particularly when the aromatic amine compounds and other amine compounds having a high stereostructual volume are employed, it is difficult to produce the carbamate at a high reaction rate, with a high selectivity and with a high yield. Further, the process (10) has big problems in that the catalyst is expensive, that the reaction rate is slow that and acid amides are produced as by-products.